Fix T51308: Bright/Contrast Doesn't respect Pre-multiplied Alpha

Brightness/contrast node was changing color but did not modify alpha
or ensured colors are premultiplied on the output. This was giving
artifacts later on unless alpha was manually converted.

Compositor is supposed to work in premultiplied alpha (except of
some really corner cases) so it makes sense to ensure premultiplied
alpha after brightness/contrast node.

This is now done as an option enabled by default, so we:

(a) Keep compatibility with old files.
(b) Have correct behavior for newly created files.

Later on we can get rid of this option.

7 files changed, 41 insertions, 2 deletions

diff --git a/source/blender/compositor/nodes/COM_BrightnessNode.cpp b/source/blender/compositor/nodes/COM_BrightnessNode.cpp
index 053f286c66e..6729571fac0 100644
--- a/source/blender/compositor/nodes/COM_BrightnessNode.cpp
+++ b/source/blender/compositor/nodes/COM_BrightnessNode.cpp
@@ -31,7 +31,9 @@ BrightnessNode::BrightnessNode(bNode *editorNode) : Node(editorNode)
 
 void BrightnessNode::convertToOperations(NodeConverter &converter, const CompositorContext &/*context*/) const
 {
+	bNode *bnode = this->getbNode();
 	BrightnessOperation *operation = new BrightnessOperation();
+	operation->setUsePremultiply((bnode->custom1 & 1) != 0);
 	converter.addOperation(operation);
 	
 	converter.mapInputSocket(getInputSocket(0), operation->getInputSocket(0));
diff --git a/source/blender/compositor/operations/COM_BrightnessOperation.cpp b/source/blender/compositor/operations/COM_BrightnessOperation.cpp
index 33e35c3fe3b..c7ba86b66bc 100644
--- a/source/blender/compositor/operations/COM_BrightnessOperation.cpp
+++ b/source/blender/compositor/operations/COM_BrightnessOperation.cpp
@@ -29,7 +29,14 @@ BrightnessOperation::BrightnessOperation() : NodeOperation()
 	this->addInputSocket(COM_DT_VALUE);
 	this->addOutputSocket(COM_DT_COLOR);
 	this->m_inputProgram = NULL;
+	this->m_use_premultiply = false;
 }
+
+void BrightnessOperation::setUsePremultiply(bool use_premultiply)
+{
+	this->m_use_premultiply = use_premultiply;
+}
+
 void BrightnessOperation::initExecution()
 {
 	this->m_inputProgram = this->getInputSocketReader(0);
@@ -64,11 +71,16 @@ void BrightnessOperation::executePixelSampled(float output[4], float x, float y,
 		delta *= -1;
 		b = a * (brightness + delta);
 	}
-	
+	if (this->m_use_premultiply) {
+		premul_to_straight_v4(inputValue);
+	}
 	output[0] = a * inputValue[0] + b;
 	output[1] = a * inputValue[1] + b;
 	output[2] = a * inputValue[2] + b;
 	output[3] = inputValue[3];
+	if (this->m_use_premultiply) {
+		straight_to_premul_v4(output);
+	}
 }
 
 void BrightnessOperation::deinitExecution()
diff --git a/source/blender/compositor/operations/COM_BrightnessOperation.h b/source/blender/compositor/operations/COM_BrightnessOperation.h
index 22086ae11e8..ff492f2b102 100644
--- a/source/blender/compositor/operations/COM_BrightnessOperation.h
+++ b/source/blender/compositor/operations/COM_BrightnessOperation.h
@@ -34,6 +34,8 @@ private:
 	SocketReader *m_inputBrightnessProgram;
 	SocketReader *m_inputContrastProgram;
 
+	bool m_use_premultiply;
+
 public:
 	BrightnessOperation();
 	
@@ -52,5 +54,6 @@ public:
 	 */
 	void deinitExecution();
 
+	void setUsePremultiply(bool use_premultiply);
 };
 #endif
diff --git a/source/blender/editors/space_node/drawnode.c b/source/blender/editors/space_node/drawnode.c
index bbbbad41aa0..f58b4050834 100644
--- a/source/blender/editors/space_node/drawnode.c
+++ b/source/blender/editors/space_node/drawnode.c
@@ -2478,6 +2478,11 @@ static void node_composit_buts_sunbeams(uiLayout *layout, bContext *UNUSED(C), P
 	uiItemR(layout, ptr, "ray_length", UI_ITEM_R_SLIDER, NULL, ICON_NONE);
 }
 
+static void node_composit_buts_brightcontrast(uiLayout *layout, bContext *UNUSED(C), PointerRNA *ptr)
+{
+	uiItemR(layout, ptr, "use_premultiply", 0, NULL, ICON_NONE);
+}
+
 /* only once called */
 static void node_composit_set_butfunc(bNodeType *ntype)
 {
@@ -2705,6 +2710,8 @@ static void node_composit_set_butfunc(bNodeType *ntype)
 		case CMP_NODE_SUNBEAMS:
 			ntype->draw_buttons = node_composit_buts_sunbeams;
 			break;
+		case CMP_NODE_BRIGHTCONTRAST:
+			ntype->draw_buttons = node_composit_buts_brightcontrast;
 	}
 }
 
diff --git a/source/blender/makesrna/intern/rna_nodetree.c b/source/blender/makesrna/intern/rna_nodetree.c
index 60b75fca689..22d07d739cd 100644
--- a/source/blender/makesrna/intern/rna_nodetree.c
+++ b/source/blender/makesrna/intern/rna_nodetree.c
@@ -5239,6 +5239,16 @@ static void def_cmp_luma_matte(StructRNA *srna)
 	RNA_def_property_update(prop, NC_NODE | NA_EDITED, "rna_Node_update");
 }
 
+static void def_cmp_brightcontrast(StructRNA *srna)
+{
+	PropertyRNA *prop;
+
+	prop = RNA_def_property(srna, "use_premultiply", PROP_BOOLEAN, PROP_NONE);
+	RNA_def_property_boolean_sdna(prop, NULL, "custom1", 1);
+	RNA_def_property_ui_text(prop, "Convert Premul", "Keep output image premultiplied alpha");
+	RNA_def_property_update(prop, NC_NODE | NA_EDITED, "rna_Node_update");
+}
+
 static void def_cmp_chroma_matte(StructRNA *srna)
 {
 	PropertyRNA *prop;
diff --git a/source/blender/nodes/NOD_static_types.h b/source/blender/nodes/NOD_static_types.h
index e754d063397..02422a8622a 100644
--- a/source/blender/nodes/NOD_static_types.h
+++ b/source/blender/nodes/NOD_static_types.h
@@ -179,7 +179,7 @@ DefNode( CompositorNode, CMP_NODE_DISPLACE,       0,                      "DISPL
 DefNode( CompositorNode, CMP_NODE_COMBHSVA,       0,                      "COMBHSVA",       CombHSVA,         "Combine HSVA",      ""              )
 DefNode( CompositorNode, CMP_NODE_MATH,           def_math,               "MATH",           Math,             "Math",              ""              )
 DefNode( CompositorNode, CMP_NODE_LUMA_MATTE,     def_cmp_luma_matte,     "LUMA_MATTE",     LumaMatte,        "Luminance Key",     ""              )
-DefNode( CompositorNode, CMP_NODE_BRIGHTCONTRAST, 0,                      "BRIGHTCONTRAST", BrightContrast,   "Bright/Contrast",   ""              )
+DefNode( CompositorNode, CMP_NODE_BRIGHTCONTRAST, def_cmp_brightcontrast, "BRIGHTCONTRAST", BrightContrast,   "Bright/Contrast",   ""              )
 DefNode( CompositorNode, CMP_NODE_GAMMA,          0,                      "GAMMA",          Gamma,            "Gamma",             ""              )
 DefNode( CompositorNode, CMP_NODE_INVERT,         def_cmp_invert,         "INVERT",         Invert,           "Invert",            ""              )
 DefNode( CompositorNode, CMP_NODE_NORMALIZE,      0,                      "NORMALIZE",      Normalize,        "Normalize",         ""              )
diff --git a/source/blender/nodes/composite/nodes/node_composite_brightness.c b/source/blender/nodes/composite/nodes/node_composite_brightness.c
index 62f23f417b2..26e4d3a52c9 100644
--- a/source/blender/nodes/composite/nodes/node_composite_brightness.c
+++ b/source/blender/nodes/composite/nodes/node_composite_brightness.c
@@ -46,6 +46,10 @@ static bNodeSocketTemplate cmp_node_brightcontrast_out[] = {
 	{	-1, 0, ""	}
 };
 
+static void node_composit_init_brightcontrast(bNodeTree *UNUSED(ntree), bNode *node)
+{
+	node->custom1 = 1;
+}
 
 void register_node_type_cmp_brightcontrast(void)
 {
@@ -53,6 +57,7 @@ void register_node_type_cmp_brightcontrast(void)
 	
 	cmp_node_type_base(&ntype, CMP_NODE_BRIGHTCONTRAST, "Bright/Contrast", NODE_CLASS_OP_COLOR, 0);
 	node_type_socket_templates(&ntype, cmp_node_brightcontrast_in, cmp_node_brightcontrast_out);
+	node_type_init(&ntype, node_composit_init_brightcontrast);
 
 	nodeRegisterType(&ntype);
 }